"We're running this entire website on a smaller full-time staff than your office IT department".
That sums it up pretty well. It does run the risk of people thinking that means we don't need much money, and therefore don't donate. It's difficult to get the balance right between saying how efficiently we spend money and saying how we need lots of money - the two seem, at first glance, to be mutually exclusive (they're obviously not in our case - we're just doing so much that however efficiently you spend the money, you still need a lot of it - but it still seems that way).